Steam power plant with intermediate superheating



R. LITWINOFF 3,139,868 STEAM POWER PLANT WITH INTERMEDIATE SUPERHEATING July 7, 1964 Filed Oct. 17, 1960 Jnvenfo r:

RICHARD LITWINOFF a v F ATTORN EYS United States Patent F 3,139,868 STEAM POWER PLANT WITH INTERMEDIATE SUPERHEATING Richard Litwinolf, Winterthur, Switzerland, assignor to Sulzer Freres, Societe Anonyme Filed Oct. 17, 1960, Ser. No. 62,988 Claims priority, application Switzerland Oct. 22, 1959 1 Claim. (Cl. 122476) The present invention relates to steam generation, and more particularly to steam power plants including intermediate superheating of partially expanded steam. According to the invention this intermediate superheating, hereinafter called reheating, is effected in sets of tubes formed into partitions or panels which are disposed in the radiation zone of the steam generator, and the invention provides protection to these reheater tubes against burn-out by passing through at least the reheater tube of each screen most intensely subjected to radiant heat a tube which in normal operation carries high pressure steam.

In steam plants including a superheater and a reheater disposed respectively in the radiation and convection zones of the boiler, it is known that the superheater and reheater have heat absorption characteristics which vary oppositely with changes in load, the heat absorption of the superheater increasing with decreasing load and the heat absorption of the reheater decreasing with decreasing load. The falling heat absorption characteristic of the reheater makes necessary the adoption of special measures to prevent the reheated steam temperature from dropping in the case of less than full load operation of the steam generator. Such measures, for example stack gas recycyling or temperature compensation by the injection of water, cannot be carried out without losses. It has therefore already been proposed to perform the reheating in tube panels disposed in the radiation zone of the steam generator. This requires special precautions to protect the panels from burning on firing up of the generator, since there is then no steam available to cool the tubes thereof. The invention provides such protection to the reheater tubes against burn-out.

According to the invention, an inner or inside tube is disposed within at least that tube of each reheater tube panel most intensely subjected to radiant heat, and this inside tube is arranged for the flow of high pressure steam therethrough, for example by connecting it between adjacent superheaters of the steam generator. During starting up, unevaporated water capable of absorbing radiant heat flows at high pressure through the inner tubes so disposed within one or more tubes of each reheater tube panel. This new arrangement insures adequate cooling of the reheater tube panels against burning during starting up. Moreover, the difliculties associated with the different heat absorption characteristics of superheaters and reheaters as functions of the load are obviated in a simple manner by the invention.

In a further development of the invention the protection against reheater tube burn-out is combined with good heat exchange between the high pressure steam and partially expanded steam during normal operation of the plant, i.e., after starting up. To this end not only the tube at the edge of the reheater tube panels most intensely subjected to radiant heat, but also adjacent tubes therein are provided with one or more tubes inside them through which high pressure steam flows. In normal operation, the partially expanded steam which flows through the space between the inner and outer tubes is heated both by the products of combustion outside the outer tube and by the high pressure steam flowing through the inside tube. The reheater heat exchange surface can in this way be made 3,139,868 Patented July 7, 1964 smaller than would be necessary if the inside tubes carrying high pressure steam were not employed.

The invention is applicable to steam generation employing working substances other than water. As hereinafter employed, the terms steam and water are to be understood as including the gaseous and liquid phases of any suitable working substance.

Further features of the invention will be apparent from the following description of exemplary embodiments of the invention, which is to be taken in conjunction with the accompanying drawing, wherein:

FIG. 1 is a diagrammatic vertical section of a steam generator plant, according to the invention, taken on the line AB in FIG. 2;

FIG. 2 is a cross-section of the steam generator of FIG. 1 taken on the line C-D in FIG. 1;

FIG. 3 is a detail of the steam generator of FIGS. 1 and 2 showing at an enlarged scale the cross sectional arrangement of certain of the tubes therein; and

FIG. 4 is a view similar to that of FIG. 3 but showing a modified construction according to the invention.

Wtih reference to FIG. 1, the steam generator 1 comprises a combustion chamber 2 and a gas stack 3, in which a plurality of heat-exchange surfaces are disposed. In the bottom part of the cumbustion chamber 2 there are provided a plurality of movable burners 4 for the combustion of fuel, only one burner being shown for the sake of simplicity. The heat produced by the burners 4 is transmitted to the heat-exchange surfaces in the combustion chamber 2 primarily by radiation and to the heat-exchange surfaces in the stack 3 primarily by convection from the products of combustion as they flow through the steam generator in the direction of the curved arrows. The walls of the combustion chamber are lined with tubes 5 in a manner known per se, the tubes on each wall being connected in parallel by means of headers 6, 7, 8 and 9. The roof bounding the combustion chamber 2 is similarly lined with tubes 28 which are connected in parallel by means of headers 29. In the transitional region 25 between the combustion chamber 2 and the stack 3 and in the stack inself there are disposed four heat-. exchange surfaces 21, 22, 23 and 24, shown diagrammatically in FIG. 1. As shownin FIG. 2, these comprise coils disposed transversely to the direction of flow of the gases. The heating surfaces 22 and 23 form first and second economizers respectively, and the heating surfaces 21 and 24 form parts of a superheater.

In the upper part of the combustion chamber 2 there are provided five panels 10, built up of tubes to form each panel into a substantially flat plane shape, oriented generally parallel to the direction of gas flow, and extending entirely across the chamber 2 at one part thereof, as indicated by FIGS. 1 and 2. The tube panels 10 serve for reheating of the steam which has been partially expanded in the high-pressure portion 30 of a plural stage prime mover or steam consuming machine such as a turbine which drives an electrical generator 32.

Each of the panels 10 comprises two sets of tubes 11 and 12. The set 11 is in the example illustrated made up of six tubes 26 which are connected in parallel by headers 13 and 14. Starting from the header 13, tubes 26 extend downwardly into the combustion chamber where they are repeatedly convoluted and then lead out of the combustion chamber to the header 14. The tube set 12, which is disposed in the same plane as the tube set 11, comprises five tubes 20, which are connected in parallel by way of headers 15 and 16 and which have a larger diameter than the tubes 26 of the set 11, as illustrated in FIG. 3. For the sake of simplicity, FIG. 3 shows only a few of the tubes 26. The tubes 20 of the set 12 are bent through a right angle. The tubes 20 thus bent, are

disposed on the side of the tube set 11 most intensively subjected to the radiation in the combustion chambers 2. Inside each tube 20 is disposed a tube 17 through which flows high-pressure steam. All the tubes 17 of the set 12 are connected in 'parallel by the headers 18 and 19 and form part of a superheater.

From a feed tank (not shown), a feed pump 33 supplies water first to the two economizers 22 and 23 and then by way of a header 7 to the tubes forming the lining of the combustion chamber Walls. The water evaporates in these tubes and is then fed by the header 6 to the superheater 24. The high-pressure steam to be further superheated passes thence through the headers 19 of the panels 10, into the tubes 17 disposed inside the tubes 20 and then leaves tubes 17 by way of the headers 18, whereupon the steam flows through the superheater 21 and finally passes to the high-pressure part 30 of the turbine.

The steam which is to be reheated after partial expansion in the high-pressure turbine 30 flows through the headers 16 of the panels into the tubes 20 of the set 12 in each panel and absorbs heat while flowing through the annulus between the inner tubes 17 and the tube 20 surrounding tubes 17. It then flow through the headers out of the tube sets 12. The partially expanded steam then flows through the headers 14 into the tubes 26 of the set 11 in each screen, where it is further reheated. After emerging from the headers 13 the steam passes to the low-pressure part 31 of the turbine, with the interposition if necessary of further reheating at heat-exchange surfaces not shown which are disposed in the convection zone of the steam generator. The steam is then further expanded in the low-pressure turbine and is thereafter condensed in the condenser 34. The condensate is taken to the feed tank.

On starting up of the plant, it is primarily non-evaporated water which is fed through the inner tubes 17, so that the tubes of the reheater tube panels 10 are adequately cooled.

FIG. 4 illustrates a modified form of construction according to the invention in which, in order to obtain improved cooling of the outer tube in the set 12 at the edge of the screen subjected to the most intense radiation, this outermost tube, identified at reference character is of larger diameter than the other tubes 20 of the set 12, the inner tube 17 within the tube 20 being of the same diameter as the inside tubes 17 provided within the other tubes 20 of the set 12.

While the invention has been described herein in terms of a number of preferred embodiments, the invention is not limited to the details of construction thus illustrated and described, but is rather set forth in the appended claim.

I claim:

A steam power plant comprising a combustion chamber, fuel combustion means in said chamber, series-connected evaporating means and superheating means for the evaporation and superheating respectively of a vaporizable working substance such as water, said evaporating means and superheating means being disposed to absorb heat from the combustion of fuel in said chamber, and reheating means for steam partially expanded in a high pressure stage of a plural-stage steam consuming machine, said reheating means comprising a plurality of tube panels disposed in the upper part of said combustion chamber, each of said tube panels comprising two pluralities of parallel-connected tubes, the tubes of each plurality being closely spaced from each other in a common plane extending substantially parallel to the direction of flow of the products of combustion from said combustion means through said combustion chamber, the tubes of the two pluralities of each panel lying moreover in a common plane, the two pluralities of tubes of each of said panels being connected in series with the tubes of the plurality most intensely subjected to radiation from said combustion means being upstream of the other plurality for flow of said partially expanded steam through said reheating means, said tube panels being exposed to radiation from said combustion means, said plant further comprising within the tubes of the plurality of parallel-connected tubes of each of said panels most intensely subjected to radiation from said combustion means a tube connected for flow of Working substance therethrough between said evaporating means and the input to said high pressure stage.

References Cited in the file of this patent UNITED STATES PATENTS 2,602,433 Kuppenheimer July 8, 1952 2,685,279 Caracristi Aug. 3, 1954 2,685,280 Blaskowski Aug. 3, 1954 2,802,114 Artsay Aug. 6, 1957 2,878,791 Lieberherr Mar. 24, 1959 2,983,262 Lieberherr May 9, 1961 

